The latest discovery is a small but not-insignificant message Kaepernick made in practice on August 10, when he wore socks that depicted police officers as cartoon pigs.

It seems to have gone almost completely unnoticed until recently.

Ben Margot/AP

A closer look in this photo, where he was stretching next to fellow quarterback Blaine Gabbert:

Ben Margot/AP

Cam Inman of the Bay Area News Group tweeted a picture of Kaepernick that day, and the socks can also been seen:

Kaepernick took to Instagram on Thursday to explain the socks:

Kaepernick has spoken openly about his protest and about police brutality in the US.

"There's a lot of things that need to change," Kaepernick said on Sunday (via the San Francisco Chronicle). "One specifically? Police brutality. There's people being murdered unjustly and not being held accountable. People are being given paid leave for killing people. That's not right."

Kaepernick also said that police officers needed more training.

Many have not approved of Kaepernick's statements. Martin Halloran, the San Francisco Police Officers Association president, said in a letter that Kaepernick had "embarrassed himself, the 49ers organizations and the NFL based on a false narrative and misinformation that lacks any factual basis."